1. Field of the Invention
This invention relates primarily to superconducting dynamoelectric machinery, and more specifically, this invention relates to structure for supporting and shielding a rotating superconducting field winding.
2. Description of the Prior Art
It is known that when certain materials, referred to as superconductors, are cooled to near absolute zero, they exhibit a complete loss of electrical resistance. Practical utilization of the zero resistance character of superconductive materials at cryogenic temparatures has recently been applied to dynamoelectric machinery. The development of the intrinsicly stable multi-filamentary superconductor has made it possible to build stable superconducting windings with relatively high transport current densities in large direct current fields.
The use of the superconductive direct current field winding considerably increases the field magnetomotive force generated by the windings and provides greatly increased flux densities in the active air gap of the machine. This increase in flux density obtains considerably increased power density and consequential reductions in the weight and volume of the machine. Thus higher ratings for turbine generators can be obtained without prohibitive increases in frame size.
The rotor structure of conventional superconducting generators is tubular as contrasted to the solid rotor structure of normally conducting generators. The tubular construction provides a reduction in weight as well as providing structural support, shielding, vacuum containment, and torque coupling. One tubular configuration which has been successfully utilized in a 5 MVA superconducting generator was constructed of a pair of inner and outer cylinders, one concentrically disposed within the other. In this construction the outer cylinder served as a supporting member and the inner cylinder served as a damper shield to protect the superconducting winding from the alternating stator fields existing externally of the rotor and to provide electrical damping for stability similar to that resulting from the rotor damper winding of a conventional generator. In this arrangement the cylinders were secured only at their end portions which permitted slight radial and axial displacement of one cylinder with respect to the other during rotation. As the rotor assemblies for superconducting machines are increased in diameter and length and operated at substantially higher rotational speeds, the effect of misalignment between the two cylinders becomes more significant and it becomes more difficult to maintain a stable moment of inertia about the principal axis of the rotor. Thus it would be desirable to provide an integrated rotor structure wherein the outer supporting cylinder and inner damping shield would perform mechanically as a single structure and thereby reduce the effective number of cylinders constituting the complete rotor assembly.